Combustion Synthesis of PrBa2Cu3O7−δ and YBa2Cu3O7−δ cuprate materials

PrBaCuO and YBaCuO cuprate materials were prepared from cooper, barium peroxide, and yttrium/praseodymium oxide by SHS and standard solid-state synthesis. SHS reactions were carried out using relatively large cooper particles (< 63 im) to obtain small product samples (13 mm in diameter). High ambient temperature was used to stabilize a combustion front in the ignited pellets. Explored was the effect of cooper particles size, starting density, and ambient temperature on phase evolutions in synthesized materials.     

Wetting and spreading of Ca-Y-Ba-Cu-O solution on Y2O3 and CaSZ crucible in growing Y1-xCaxBa2Cu3O7-δ single crystal

Sizable and uniform Y_1-xCa_xBa₂Cu₃O_7-δ single crystals are of significant importance to study high-temperature superconductivity. However, the severe liquid loss resulting from intrinsic wetting property during top-seeded solution-growth (TSSG), makes it difficult to obtain such crystals. Here the reactive wetting performance of the Ca-Y-Ba-Cu-O solution on two types of crucibles was studied. It was identified that the spreading process on the Y₂O₃ crucible is characterized by forming double-layer of Y₂BaCuO₅ and YBa₂Cu₃O_7-δ, while that on the CaSZ crucible (Ca-stabilized ZrO₂) produces the BaZrO₃ layer with CuO phase. In the former case, the liquid has a low energy interface with the top layer of YBa₂Cu₃O_7-δ, leading to strong spreading and creeping behaviors. Conversely, due to a high interfacial energy between solution and BaZrO₃, the CaSZ crucible has a low wettability, particularly beneficial to solve the liquid loss problem. Consequently, with negligible liquid creeping out of CaSZ crucibles, we succeeded in growing a series of homogeneous Y_1-xCa_xBa₂Cu₃O_7-δ single crystals with an acceptable size up to a × b × c = 11.2 × 11 × 4.8 mm³. Moreover the wetting modes of solution on various kinds of crucibles for TSSG in growing doped YBa₂Cu₃O_7-δ single crystals were also elucidated. Most importantly, the understanding gained from this work is broadly applicable for producing other desirable doped-crystals.     

Quantification of the level of samarium/barium substitution in the Ag-Sm1+xBa2−xCu3O7−δ system

The high-temperature SmBa₂Cu₃O_7?δ (Sm-123) superconducting system, which is characterised by a high critical transition temperature (T_c) and a high critical current density (J_c), suffers severely from the effects of Sm/Ba substitution in the superconducting Sm-123 phase matrix, and especially so for large, single grains grown in air, resulting in a significant variation in T_c at different positions within a single grain. As a result, the suppression of Sm/Ba substitution in the Sm_1+xBa_2?xCu₃O_7?δ phase matrix (SmBCO, where x represents the Sm/Ba substitution level in the SmBCO system) is critical to achieving good superconducting properties in this material. Here we report the use of Electron Probe Micro-Analysis (EPMA) to investigate, adjust and optimise the composition of mechanically-stabilised standard Ag-SmBCO bulk single grains. We show that the substitution levels within these samples changes linearly within increasing distance from the vicinity of a single crystal seed used to nucleate the single grain growth process. In addition, we identify a constant value of x of ?0.080 for the composition-adjusted Ag-SmBCO bulk single grain. This is the first time that the quantification of the Sm/Ba substitution level in the SmBCO system has been measured accurately and directly using EPMA, and suggests clearly that the Sm/Ba substitution can be suppressed effectively in air. This research will provide significant insight into the development of a process to suppress Sm/Ba substitution even further in superconducting SmBCO single grains in the future.     

Structural and superconducting properties of Y(Ba1-xKx)2Cu3O7-δ ceramics

Y(Ba_1-xK_x)₂Cu₃O_7-δ ceramics (x = 0.00, 0.03, 0.05 and 0.08) were synthesized by thermal treatments of aqueous solution of metals nitrates and polyvinyl pyrrolidone (PVP) that acts as a capping agent. The effects of K-substitution on the crystal structure, microstructure and electrical resistance of samples were investigated. The X-ray diffractions results indicated an improvement of crystallinity and variation of lattice constant, a, b and c of YBa₂Cu₃O_7-δ (Y123) phase with K-substitution. The K-substitution resulted in increasing of orthorhombicity factor compared to pure Y123. Microstructural observation using scanning electron microscopy showed that K-substitution promotes the grain growth of Y123. The superconducting transitions (T_c) of the substituted-samples were higher than that of the pure Y123. The T_c (onset) were 93, 97, 95, 95 K for the samples with x = 0.00, 0.03, 0.05 and 0.08, respectively. Comparing with pure sample, the substituted-samples showed sharper superconducting transition (ΔT_c). The best superconducting properties was observed for sample with x = 0.03.     

State of manganese atoms in the Nd1+x Sr2−x Mn2O7−δ solid solution

The oxidation state of manganese in the Nd_2?x Sr_1+x Mn₂O_7?δ solid solution was determined by X-ray photoelectron spectroscopy and by calculating the oxygen nonstoichiometry based on the gravimetric data. As a result of the heterovalent replacement of Nd³⁺ with Sr²⁺, the change in the oxidation state of manganese occurs in different ways, i.e., it increases at x > 0 and decreases at x < 0. In the latter case, some oxygen ions acquire the oxidation state of ?1. The samples slowly cooled under oxidative conditions possess a significant positive oxygen non-stoichiometry, which tends to decrease after Nd³⁺ is replaced with Sr²⁺. An excess of oxygen stabilizes the crystal structure of Nd_1+x Sr_2?x Mn₂O_7?δ.     

Preparation of Y1−x Yb x Ba2Cu3O7−y superconducting films by chemical vapor deposition

High Tc Y_1−x Yb _x Ba₂Cu₃O_7−y films were prepared on SrTiO₃(100) substrates by chemical vapor deposition method. Yb₁Ba₂Cu₃O_7−y films were obtained at higher oxygen partial pressure compared with Y₁Ba₂Cu₃O_7−y films at the same deposition temperature. Tc,o (R=0) decreased about 1.5 K when Y was fully substituted with Yb. The caxis lattice parameter of Y_1−x Yb _x Ba₂Cu₃O_7−y films also decreased as the amount of Yb(x) increased.     

Enhanced superconducting properties of YBa2Cu3O7−δ thin film with magnetic nanolayer additions

Vertically aligned nanocomposite (VAN) (La_0.7Sr_0.3MnO₃)_0.5(CeO₂)_0.5 and pure La_0.7Sr_0.3MnO₃ layers were incorporated into YBa₂Cu₃O_7−δ (YBCO) thin films as bilayer stacks for magnetic flux pinning enhancement. The films show high epitaxial quality, suggested by XRD and TEM study. The critical temperature T_c of the bilayers is about 90 K, which is close to that of pure YBCO films, while both the self-field J_c^sf and in-field critical current density J_c^in-field are largely enhanced. Among all samples, the film with VAN cap layer shows the highest J_c values in all field ranges. This study demonstrates an effective way towards the tunable pinning effect for YBCO coated conductors by both defect and magnetic pinning.     

Superheating nature coupled with Mg-doping effect of high thermal stable NdBa2Cu3O7-δ film

NdBa₂Cu₃O_7-δ thin film deposited on a MgO substrate has been verified to remain solid above its peritectic melting temperature (T_p). Such a superheating nature is attributed to its low energy surface and epitaxial interface with substrate. Here, combining superheating nature with doping effect, we report a novel structure, Mg-doped NdBa₂Cu₃O_7-δ film with YBa₂Cu₃O_7-δ buffer layer for the first time. Remarkably, this film presents a higher thermal stability level than heretofore possible when acting as a seed for preparing SmBa₂Cu₃O_7-δ bulks by melt growth, enduring a temperature of 1128°C, 43 K above its T_p for 1 hour. The utilization of such a high T_max in melt growth is beneficial to the fabrication of large-sized and high-performance bulk in terms of effectively broadening the growth window and suppressing the heterogeneous nucleation. More importantly, some high thermal stability required technological applications, such as batch growth and failed bulk recycling, are likely to be realized by this novel Mg-doped NdBa₂Cu₃O_7-δ film seed. Finally, we show how the observed metastable phase is linked to the distinctive film architecture.     

Combustion in the Y2O3-BaO2-αCu system with gasifying additives

Burning has been examined on the system for various oxygen pressures. The value of determines whether the process accelerates or dies away. An explanation is proposed. Adding BaCO₃ as a gasifying additive enables one to avoid extensive melting and reduces the maximum temperature. The main reaction products have been identified. SHS with gasifying additive has made it possible to synthesize the tetra phase of the high-temperature superconductor Y₁₂₃, whose temperature of transition to the superconducting state T_c is dependent on the amount of additive used.Synthetic Materials Institute, Russian Academy of Sciences, Chernogolovka 142432. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 60–62, July–August, 1994.     

Reactivity of LaNi1−y Co y O3−δ Perovskite Systems in the Deep Oxidation of Toluene

In the present work we have evaluated the oxidation of toluene over different lanthanum perovskites with a general composition of LaNi_1?y Co _y O_3?δ. These catalysts, prepared by a spray pyrolysis method, have been characterised by XRD, BET and FE-SEM techniques. Additional experiments of temperature programmed desorption of O₂, reduction in H₂ and X-ray absorption spectroscopy were also performed in order to identify the main surface oxygen species and the reducibility of the different perovskites. The catalytic behaviour toward the oxidation of toluene (as a model for VOCs compounds) was evaluated in the range 100–600 °C, detecting a total conversion for all the samples below 400 °C and higher activities for the cobalt-containing perovskites. The catalytic behaviour of these samples is consistent with a suprafacial mechanism, with the α-type oxygen playing an active role in the oxidation reaction.     

Magnetic doping effects on the superconductivity of Y1-xMxBa2Cu3O7-δ (M = Fe,Co, Ni)

The discovery of superconductivity in copper oxide compounds has attracted considerable attention over the past three decades. The high transition temperature (T_c) in these compounds, exhibiting proximity to an antiferromagnetic order in their phase diagrams, remains one of the main areas of research. It is believed that magnetic fluctuations provide substance for the exotic superconductivity observed in these compounds. The present study attempts to introduce Fe, Co and Ni magnetic impurities into the superconducting cuprate YBa₂Cu₃O_7-δ with the aim of exploring the T_c behavior. The solid-state synthesis method is exploited to prepare fully oxygenated Y_1-xM_xBa₂Cu₃O_7-δ (Y_1-xM_x-123) (M = Co, Fe, Ni) samples with low levels of doping (0.00000 ≤ x ≤ 0.03000). Systematic measurements are then employed to assess the synthesized samples using AC magnetic susceptibility, electrical resistivity and X-ray diffraction (XRD). The measurements revealed an increase in T_c as a result of magnetic substitution for Y. However, the study of non-magnetic dopings on the fully oxygenated Y_1-xM'_xBa₂Cu₃O_7-δ (Y_1-xM'_x-123) (M' = Ca, Sr) samples showed a decrease in T_c. Quantitative XRD analysis further suggested that the internal pressure could have minor effects on the increase in T_c. The normal state resistivity vs temperature showed a linear profile, confirming that the samples are at an optimal doping of the carrier concentration.     

Tribological Properties of Ag/DyBa2Cu3O7-δ Superconducting Ceramics

利用摩擦实验机从液氮温度至室温对超导陶瓷 Ag/DyBa2Cu3O7–δ（Ag/Dy123）的摩擦学性能进行研究,结果表明：当温度降到液氮温度后,10% （质量分数）Ag/Dy123 超导陶瓷与不锈钢盘对摩,摩擦因数明显下降,最后稳定在 0.20 以下。对制备的 Ag/Dy123 超导陶瓷进行 X 射线衍射、扫描电子显微镜、高分辨电子显微镜、能量散射 X 射线分析,结果表明：Ag 没有影响 Dy123 的超导电性,明显改善了常温下 Dy123 的摩擦学性能,在正常载荷和滑行速率下,（5%～10%）Ag/Dy123 超导陶瓷的摩擦因数为 0.25,5%Ag/Dy123 超导陶瓷磨损率最低,为 4.02 × 10。分布在基体中的 Ag 微粒能有效抑制裂纹萌生和扩展并在摩擦作用下形成 Ag 转移膜,陶瓷硬基底承载和软金属转移膜润滑的协同作用,使材料表现出良好的减摩耐磨性能。     

Microwave dielectric properties of Bi2O3-doped Ca[(Li1/3Nb2/3)1−xTix]O3−δ ceramics

The effect of the additive on the densification, low temperature sintering, and microwave dielectric properties of the Ca[(Li_1/3Nb_2/3)_1−xTi_x]O_3−δ(CLNT) was investigated. Bi₂O₃ addition improved the densification and reduced the sintering temperature from 1150 to 900 °C of CLNT microwave dielectric ceramics. As the Bi₂O₃ content increased, the dielectric constant (ε_r) and bulk density increased. The quality factor (Q·f₀), however, was decreased slightly. The temperature coefficient of resonant frequency (τ_f) shifted to a positive value with increasing Bi₂O₃ content. The dielectric properties (ε_r, Q·f_0, τ_f) of Ca[(Li_1/3Nb_2/3)_0.95Ti_0.05]O_3−δ and Ca[(Li_1/3Nb_2/3)_0.8 Ti_0.2]O_3−δ with 5 wt.% Bi₂O₃ sintered at 900 °C for 3 were 20, 6500 GHz, −4 ppm/°C, and 35, 11,000 GHz, 13 ppm/°, respectively. The relationship between the microstructure and dielectric properties was studied by X-ray diffraction (XRD), and SEM.     

Intergranular properties of polycrystalline YBa2Cu3O7−δ superconductor added with nanoparticles of WO3 and BaTiO3 as artificial pinning centers

Pure (x = 0.0 wt%) superconducting YBa₂Cu₃O_7−δ (YBCO) sample and added YBCO sample with 0.1 wt% artificial barium titanate (BTO) and 0.1 wt% tungsten trioxide (WO₃) nanoparticles were prepared using the solid-state reaction route. Phase purity was analyzed via the X-rays diffraction technique. Scanning electron microscopy showed a high density of isolated W-rich secondary phases embedded within the YBCO added sample. Furthermore, both WO₃ and BTO nanoparticles tend to reside at the grain boundaries and play the role of bridges connecting the YBCO superconducting granules. Quantitative analysis performed on the areas where nanosized entities induced by BTO and WO₃ phases was evidenced by EDX analysis equipped with SEM instrument. The values of H_c2 increased from 1.6 T for pristine to 3.4 T for BTO/WO₃ added samples. The superconducting parameters determined by AC susceptibility measurements also showed an improvement with WO₃ and BTO nanoparticles co-addition. The value of J_cinter(0) increases from 1.18 kA/cm² for the pristine sample to 5.10 kA/cm² for BTO/WO₃ co-added sample. Hence, the incorporation of artificial BTO and WO₃ nanoparticles into the YBCO superconducting phase could be a useful way to make such compounds available in practical applications.     

Transport properties of BaCe0.85Y0.15O3−δ at closed-cycle refrigerator temperature

The electrical conducting properties of both hydrated and dehydrated BaCe_0.85Y_0.15O_3?δ (barium cerate, BCY) were investigated at low temperature (473–203 K) by an AC impedance analyzer combined with a dielectric interface. For the BCY, the bulk and grain boundary conductivities were separated with the equivalent circuit model, and the bulk conductivity was approximately two orders of magnitude higher than the grain boundary conductivity. At very low temperature (203 K), a single semicircle was obtained in the impedance plot, whereas three distinct semicircles were plotted in modulus plot due to the three different resistance components in the system. The activation energy of bulk conductivity was 0.55 eV and 0.57 eV for the hydrated and dehydrated BCY samples, respectively.     

溶胶-凝胶自蔓法制取Y1Ba2Cu3O7-x的研究

采用溶胶-凝胶自蔓法制备了超细YBa2Cu3O7-超导材料。讨论了pH的控制，溶胶-凝胶-自燃过程及样品的高温烧结。YBCO溶胶的荧光光谱进行了表征，表明溶胶粒子为纳米级；XRD分析表明制得YBCO超细粉末主要为正交YBCO相，ESEM分析表明产物均匀，性能优良。     

Iron diffusivity into superconducting YBa2Cu3O7−δ at oxygen-assisted sintering: structural,magnetic, and transport properties

Optimization of materials exhibiting high-temperature superconductivity for producing controllable nano-devices is crucial for industrial applications. Herein we report a comprehensive study of the diffusion process between YBa₂Cu₃O_7−δ (YBCO) and iron particles. Fe diffusion into the YBCO matrix could be fundamental for multilayer systems with YBCO/Fe-alloy interfaces. We have found that the orthorhombic YBCO structure adopts to 3 wt% Fe, while for higher Fe content, a formation of BaFeO_3−δ and iron oxides was observed. Complementary measurements confirmed the strong superconductivity suppression in YBCO-Fe materials containing more than 7 wt% Fe. The YBCO with diffused Fe material retain the unit cell orthorhombicity (max. 3 wt% Fe), and their superconducting properties follow the principle of critical scaling with different exponents (γ). The critical current density (J_c), pinning fields (H_P) exhibit γ = 1, the first critical field (H_c1) shows γ = 1/2, and critical temperature (T_c) demonstrates γ = 7/4.     

The effect of forming stresses on the sintering of ultra-fine Ce0.9Gd0.1O2−δ powders

The effect of particle and pore arrangement on sintering and densification of ultra-fine (～130 nm) Ce_0.9Gd_0.1O_2?δ powder was evaluated. The common understanding that higher initial density of a ceramic network leads to a higher sintered density is not valid for fine powders, which have extremely good sinterability when there is a favourable particle packing. The effect of the applied stresses during forming (which produce different particle packing arrangements) was investigated by forging green bodies by different shaping techniques, including casting, and cold isostatic pressing. Samples formed with techniques that apply low levels of stress had a particle arrangement which significantly enhanced sintering at low temperature, compared to those prepared by high stress techniques. The sample geometry, heat treatment for organic removal and the initial density of the green body had a negligible effect on the final density when the ratio of the pore size to particle size was around 1.     

Microstructures and photovoltaic effect of KNbO3–SrCo0.5Hf0.5O3−δ ferroelectric semiconductors

Polarization is one of the unique properties of ferroelectric materials; yet the polarization mechanism for enhancing ferroelectric photovoltaic performance is rarely been investigated, particularly in terms of bandgap variation. In this work, the effect of high-field polarization on the enhanced photovoltaic performance of a ferroelectric ceramic, 0.98KNbO₃–0.02SrCo_0.5Hf_0.5O_3−δ (KNSCH2), was explored in terms of bandgap variation. The bandgap of the KNSCH2 sample shrank after polarization because of the increase in potential energy band overlap and the upward shift of the valence band due to increased oxygen-vacancy defects. The polarization optimized the energy band structure of KNSCH2, promoting the separation and transport of photoinduced carriers and thus further enhancing its photovoltaic performance. The KNSCH2 sample shows a twofold enhancement in J_sc after 60 kV/cm polarization. The degree of the lattice distortion of KNSNH2 increased following polarization, causing a minute increase in its cell asymmetry. The reasons for the bandgap narrowing and the creation of sub-bandgaps in the KNSCH samples were also investigated. This work opened new doors to understanding the mechanisms underlying the polarization-enhanced photovoltaic performance of ferroelectric materials.     

The influence of inter-granular coupling on the magnetic susceptibility and critical current density of YBa2(Cu1−xAgx)3O7−δ superconductors prepared by ethylene glycol assisted solvothermal approach

Series of YBa₂(Cu_1−xAg_x)₃O_7−δ (0≤x≤0.09) powders were prepared by ethylene glycol assisted solvothermal approach. X-ray diffraction verified the formation of single phase crystal structure for all the investigated samples, implying the complete solubility of the silver ions into YBa₂Cu₃O₇. The partial substitution of the Ag atoms into the Cu sites caused a decrease of the lattice constant (c) and an increase of the lattice constants, a, and, b, to preserve the orthorhombic crystal structure of YBa₂Cu₃O₇. The scanning electron microscopy depicted that the incorporation of silver ions into copper sites adjusts the random orientations of the YBCO grains and suppresses the formation of grain boundary. The AC magnetic susceptibility measurement revealed that the superconducting performance of the YBa₂Cu₃O₇ is preserved at all Ag concentrations. The critical current density, J_c, measurement revealed that the addition of the Ag into the YBCO caused a strong pinning force is established due to the strong coupling among the grains instead of the weak Josephson junctions and in turn a remarkable increase of the zero field J_c from 2.7 MA/cm² to 9.1 MA/cm² was achieved.